In U.S. Pat. No. 3,852,194, issued to me on Dec. 3, 1974, an apparatus for fluid collection and partitioning is shown as including an evacuated container or vessel having a closed end with gel-like material positioned therein and an open end sealed by a needle-puncturable stopper. A fluid having differing density phases such as blood is siphoned into the vessel through the stopper, and centrifugation is applied to the vessel to separate the fluid into at least two phases. The gel-like material is preferably thixotropic and has a specific gravity or density which is intermediate the densities of the two phases to be separated and accordingly moves during centrifugation to an interface position between the phases. After centrifugation, the material is adapted to form a physical and chemical seal or partition with the vessel sidewalls between the separated phases, which permits the light phase of the multiphase fluid to be simply decanted from above the material.
Such apparatus and method permits blood to be collected, centrifuged, and physically partitioned without removal of the stopper. It will be appreciated that this closed method is of great advantage to hospital or laboratory personnel, not only due to its convenience but also to its inherent protection against infections from contact with contents of the separation vessel. However, the gel-like partitioning material restricts access to the heavy red cell phase between it and the bottom end of the tube.
A main feature of the present invention is the provision of an access device which may be used in a partially evacuated collection and separation apparatus to provide, after centrifugation, access through the partitioning material to at least a sample quantity of the separated heavy phase below the partitioning material.
Although the heavy phase access device of the present invention has particular use in the closed collection and separation devices generally described above, it is also useful in centrifugal separation systems wherein the partitioning material is added to the separation container after collection of the multiphase fluid. Further, it may be used in systems which utilize any kind of inert barrier fluid or semi-fluid of a selected density to form a fluid or semi-fluid barrier between phases of a specimen fluid upon centrifugation of the specimen fluid into its phases. For example, the access device could be used in a silicone oil flotation method of fractionating cellular matter from body fluids. In such a method, which is believed to have been first described by S. H. Seal in Cancer (1959, 12:590-595), a blend of silicone oils is used in an "open" sequence to form a fluid barrier between two phases. The access device of the present invention may be used to provide access to, and removal of, the heavy phase below the fluid barrier. The device is also useful in a beads-plus-adhesive separator assembly, such as described in U.S. Pat. No. 3,920,557, wherein a mixture of adhesive and beads is distributed from an upper end of the centrifugation vessel.